1. Field of the Invention
The present invention is related to a transflective electrophoretic display and a method for manufacturing the same, and more particularly, to a display structure that changes the behavior of charged pigment particles via adjustment of an electric field and a method for manufacturing the display structure.
2. Description of Related Art
An electrophoretic display adjusts an electric field to control the distribution of charged particles to change its display regions' reflectance for ambient light and thus to display images. The electrophoretic display is flexible and the images shown on the electrophoretic display can be viewed by using ambient light. Furthermore, the electrophoretic display can be made by using a roll-to-roll manufacturing procedure. It is thus convenient for mass production and its cost can also be reduced. Moreover, the visual angle of the electrophoretic display is unlimited. Hence, the images shown on the electrophoretic display can be viewed from any angle. In addition, the electrophoretic display is insensitive to spacing variation of substrates and possesses bistability. Hence, the technology of the electrophoretic display is vital for development of flexible displays or electronic papers.
In general, the surfaces of particles can be charged via the dissociation per se or absorption of other charged materials. When the charged particles are put in an electric field, they drift toward an oppositely charged pole. This phenomenon is called electrophoresis. The speed of electrophoresis alters with the categories, diameters, and concentration of charged particles, the intensity, distribution, and direction of external electric fields, and the categories of display solvents. The electrophoretic display shows the images by using the properties of electrophoresis.
U.S. Pat. No. 6,750,844 discloses an electrophoretic display structure. This patent discloses a transparent film made with microcapsules and coated with an adhesive material. The microcapsules include display solvent with white and black particles having opposite electric poles. The transparent film is disposed on a substrate with a driving circuit to provide a display device. U.S. Pat. No. 6,751,007 and 6,750,844 further disclose an electrophoretic display structure with separating walls. The separating walls are formed between display units to make the display structure stronger than the previous one. The shape, size, and proportion of the separating walls determine the implementation manner of the display structure. Hence, the separating walls are the main members of the display structure. The rooms formed between the separating walls are filled with an electrophoretic display solvent having pigment particles. Moreover, by using a microcup technology proposed in these two patents, the edge-sealing limitation of the display units is removed and the display structure has a better image-displaying quality. Besides, by using the microcup technology, the display solvent is effectively confined to specific rooms and the display structure can be made flexible.
A transflective electrophoretic display is disclosed in U.S. Pat. No. 6,751,007. The display device has multiple display cells 103 separated by separating walls 109. FIG. 1A shows a display cell 103 of the transflective electrophoretic display. The display cell 103 has a top transparent layer 101 and a bottom electrode plate 102 and is surrounded by the separating walls 109. The room formed between the separating walls 109 is filled with a dielectric display solvent 105 having multiple charged pigment particles 104. A sealing layer 106 is provided on the dielectric display solvent 105 to confine it to the room formed between the separating walls 109. The display cell 103 is thereby completed. In addition, a backlight module 107 is provided to assist the electrophoretic display device to display images.
In the prior art shown in FIG. 1A, in order to perform the display function, the charged pigment particles 104 of the dielectric display solvent 105 are controlled by the electric field provided by the top and bottom substrates, i.e. the top transparent layer 101 and the bottom electrode plate 102. The electric field is provided in accordance with an up/down switching mode, an in-plane switching mode, and a dual switching mode. As shown in FIG. 1A, the top substrate is made of ITO glass. The bottom substrate includes in-plane electrodes 110a and 110b, bottom electrodes 111, and gaps 112.
The technology for providing in-plane electric fields can be found in U.S. Pat. No. 6,639,580, “Electrophoretic Display Device and Method for Addressing Display Device.” The in-plane electric field is produced via the in-plane electrodes disposed on the substrate, i.e. the first and second display electrodes. The charged pigment particles of the electrophoretic display solvents are controlled by the electric fields to perform the display function.
Reference is made to FIG. 1B, which shows an embodiment of the prior art disclosed in U.S. Pat. No. 6,751,007. The display structure shown in FIG. 1B has multiple microcups, i.e. display cells 103, which form a rectangular array.
U.S. Pat. No. 6,751,007 further discloses a color display structure. As shown in FIG. 2A, each color display cell 20 of the display structure at least has three display sub-cells for providing blue light, red light, and green light, respectively. The colorless display solvent 25 includes multiple white charged pigment particles 24 for scattering light emitted from a backlight module (not shown). The sub-cells have a red color filter 21, a green color filter 22, and blue color filter 23, respectively.
The electrodes of the bottom substrate are controlled to provide different electric fields to control the charged pigment particles 24 to change the light-scattering extents of the sub-cells. The filters 21, 22, and 23 are used to produce color lights via their light-filtering functions, respectively. Thus, various color effects are provided.
The white charged pigment particles 24 can be replaced by black charged pigment particles capable of absorbing light. In this way, another display structure with a contrary color-generating operation is provided.
Reference is made to FIG. 2B, which shows another color display structure of the prior art. The color display cell 20 includes three display sub-cells for providing blue light, red light, and green light, respectively. The colorless display solvent 25 includes multiple color charged pigment particles. The color charged pigment particles include red charged pigment particles 26, green charged pigment particles 27, and blue charged pigment particles 28. The color display cell 20 has a white or black back plate 29. The electrodes of the bottom substrate are controlled to provide different electric fields to control the color charged pigment particles 25, 27, and 28 to change the light-scattering extents of the sub-cells. Thus, various color effects are provided.
Most conventional electrophoretic display devices are reflective display devices. However, this type of display devices cannot show images when ambient light is insufficient or doesn't exist. On the other hand, transmittance electrophoretic display devices use the electrophoretic display media as light shutter, only. Color light needs to be produced by using color filters together with backlight modules. Thus, the power consumption of transmittance electrophoretic display devices is so large that made this display not suitable for mobile device applications.
The transflective electrophoretic display disclosed in U.S. Pat. No. 6,751,007 uses the separating walls 109 as a medium for light transmission. In this way, the electrophoretic display can be viewed even in darkness. However, the separating walls 109 may leak light. Furthermore, in this display device, the light emitted from the backlight module doesn't pass through the display solvent directly and is only used for illumination. Hence, this display device doesn't have a high display quality. At the same time, it adopts a dual-mode driving mechanism. Hence, this display device is complicated in design and has a difficult manufacturing process.